Submersible disk-type pump for viscous and solids-laden fluids having helical inducer

ABSTRACT

A submersible pump assembly configured to manipulate the flow of fluids to achieve sufficient flow rate and fluid pressure to efficiently pump viscous or solids-laden fluid, while minimizing the risk of pump clogging and/or damage due to the solids content of the fluid. The submersible pump assembly comprising a cylindrical housing having an intake disposed at an upstream end for receiving viscous and/or solids-laden fluid and an outlet disposed at a downstream end opposite the intake for discharging the fluid to the surface. A rotating shaft extending through the cylindrical housing along a center axis of the housing and adapted to be driven by a submersible motor. A plurality of successive pumping stages disposed in a co-axial arrangement along the rotating shaft and a helical inducer coupled to the shaft between the intake and the plurality of pumping stages. The helical inducer comprising at least a single helical turn that directly converges into the plurality of pumping stages.

FIELD OF THE INVENTION

The present disclosure relates to the field of submersible pumps and, in particular, to a submersible disk-type pump assembly having a helical inducer for pumping viscous and solids-laden fluids.

BACKGROUND OF THE INVENTION

Submersible pumps, and in particular electrical submersible pump (ESP) systems, are known as an effective artificial lift method for pumping production fluids to the surface. ESP systems typically include an electric motor and a multi-stage centrifugal pump operating in a vertical position and run on a production string, connected back to a surface control mechanism and transformer via an electric power cable. The multi-stage centrifugal pump typically consists of stages of rotating impellers and stationary diffusers mounted on a single shaft. As the impellers are rotated, fluid is passed to the eye of the next impeller through the respective diffuser. As the fluid leaves the impeller, the liquid kinetic energy and the velocity in it is transformed to static pressure, leading to an amplified pressure on the downstream side of the pump. In a multi-stage system, pressure is increased as fluid is pumped from one impeller to the next to push the fluid upwards.

Viscous and solids-laden fluids present challenges for ESP systems. In particular, the high internal friction arising with viscous and solids-laden fluids typically results in significant performance inefficiencies. As well, the abrasive materials in such fluids results in rapid solids impingement wear and eventual loss of performance. The development of a number of modifications to ESP systems have been described for addressing these challenges.

Commonly invented U.S. Pat. No. 6,227,796 describes a modification to the pump impeller that can be used in a multi-stage pump system to manipulate the flow patterns at the radial periphery of the impeller so as to significantly reduce head losses in the annular flow chamber. Specifically, an impeller comprising a stack of circular disks is described that form a frusto-conical profile between the upstream and downstream ends. In this way, the disks form a plurality of radial flow passages wherein incrementally less fluid issues from each successive radial flow passage between adjacent disks thereby reducing head loss in the issuing viscous fluid flow and increasing pumping efficiency. Solely by modifying the impeller, fluid flow is manipulated at the impeller stage to improve efficiency in a submersible pump system.

United States Patent Publication No. 2012/0269614 relates to a staged centrifugal pump (as opposed to a staged disk-type pump and of the present invention) and attempts to improve pump efficiency of such centrifugal pump by manipulating fluid flow at intake. In particular, there is described an auger assembly coupled to the shaft leading to the first centrifugal pump stage. The auger assembly comprises a helical portion terminating into a plurality of radial blades that lead into the multi-stage impellers. The auger is described as creating a contained tight vortex of fluid that keeps solids suspended in the fluid and increases velocity of the fluid into the eye of a diffuser. The auger further acts to break up solids to further facilitate fluid flow. In this way, solids are kept from accumulating and “plugging” flow in the lower stages of the multi-stage centrifugal pump stack, and as a result, reduce the amount of abrasive wear.

There continues to be a need for a submersible disk-type pump system that is resistant to the abrasiveness of solids-laden fluids, while still able to achieve flow and pressure requirements sufficient for efficient production of viscous fluids comparable to centrifugal stage pumps.

This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

SUMMARY OF THE INVENTION

Disclosed herein are exemplary embodiments pertaining to a submersible pump assembly for viscous and solids-laden fluids. In accordance with one aspect of the present disclosure, there is described a submersible pump assembly for pumping a viscous or solids-laden fluid upwardly, comprising: a cylindrical housing having an intake disposed at an upstream end and an outlet disposed at a downstream end opposite the intake; a rotating shaft extending through the cylindrical housing along a center axis of the housing and adapted to be driven by a submersible motor; a plurality of successive pumping stages disposed along the rotating shaft in a co-axial arrangement, each pumping stage comprising a frusto-conical disk impeller and a diffuser; and a helical inducer coupled to the shaft at the upstream end disposed between the intake and the plurality of pumping stages, the inducer comprising at least a single helical turn that directly converges into the plurality of pumping stages.

In accordance with another aspect, there is described a submersible pump assembly for pumping a viscous or solids-laden fluid upwardly, comprising: a cylindrical housing having an intake disposed at an upstream end and an outlet disposed at a downstream end opposite the intake; a rotating shaft extending through the cylindrical housing along a center axis of the housing and adapted to be driven by a submersible motor; a plurality of successive pumping stages disposed along the rotating shaft in a co-axial arrangement, each pumping stage comprising a frusto-conical disk impeller and a diffuser, the frusto-conical disk impeller comprising a stack of axially spaced apart circular disks of progressively decreasing radii towards the downstream end, each disk extending radially and concentrically from a cylindrical core for receiving the rotating shaft therethrough, the cylindrical core comprising a plurality of parallel flow passages spiraling axially about the cylindrical core and communicating with a plurality of radial flow passages formed between the disks, wherein fluid flows from the upstream end of the impeller through the axial flow passages and into the radial flow passages between disks; and a helical inducer coupled to the shaft at the upstream end disposed between the intake and the plurality of pumping stages, the inducer comprising at least a single helical turn that directly converges into the plurality of pumping stages.

In accordance with a further aspect, there is described a method for pumping a viscous or solids-laden fluid upwardly, comprising: providing the submersible pump assembly according to embodiments described herein, and a motor configured to drive the pump assembly; positioning the submersible pump assembly in a wellbore; activating the motor to actuate the submersible pump assembly; wherein viscous or solids-laden fluid enters the submersible pump assembly to be homogenized by the helical inducer to break up any solids in the fluid while accelerating and directing the fluid into the plurality of successive pumping stages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings.

FIG. 1 is a cross-sectional view of a pump assembly, according to embodiments of the present disclosure;

FIGS. 2A and 2B are cross-sectional and perspective views of a prior art conical impeller shown as part of the pump assembly illustrated in FIG. 1, according to embodiments of the present disclosure;

FIGS. 3A and 3B are partial cross-sectional and top views of the prior art conical impeller shown in FIGS. 2A and 2B, according to embodiments of the present disclosure;

FIGS. 4A and 4B are perspective views of a single helix inducer, according to embodiments of the present disclosure;

FIGS. 5A and 5B are top and cross-sectional views of the single helix inducer shown in FIGS. 4A and 4B, according to embodiments of the present disclosure;

FIGS. 6A and 6B are perspective views of a double helix inducer, according to embodiments of the present disclosure;

FIGS. 7A and 7B are top and cross-sectional views of the double helix inducer shown in FIGS. 6A and 6B, according to embodiments of the present disclosure;

FIG. 8 is a graphical representation of the effect of an inducer at intake on performance and system efficiency of a prototype frusto-conical stage disk-type pump, according to embodiments of the present disclosure, with water, at 25° C., 3500 RPM, no charge pump (200-Performance with Inducer, Standard Diffuser; 210-Performance with Inducer, Modified Diffuser; 220-Performance with No Inducer, Standard Diffuser; 400-Efficiency with Inducer, Standard Diffuser; 410-Efficiency with Inducer, Modified Diffuser; 420-Efficiency with No Inducer, Standard Diffuser); and

FIG. 9 is a graphical representation of the effect of rotation direction on performance and system efficiency of a prototype frusto-conical stage disk-type pump, according to embodiments of the present disclosure, with water, at 25° C., 3500 RPM, no charge pump, and with a standard diffuser (500-Performance with Clockwise Rotation; 510-Performance with Counter-Clockwise Rotation; 600-Efficiency with Clockwise Rotation; 610-Efficiency with Counter-Clockwise Rotation).

DETAILED DESCRIPTION OF THE INVENTION

The submersible disk-type pump assembly according to embodiments of the present disclosure is configured to manipulate the flow of fluids to achieve sufficient flow rate and fluid pressure to efficiently pump viscous or solids-laden fluid upwardly, while minimizing the risk of pump clogging and/or damage due to the solids content of the fluid. The submersible pump assembly of the present disclosure, provides a coupled approach to addressing the particular challenges presented by viscous or solids-laden fluid. According to embodiments described herein, the submersible pump assembly is configured to manipulate fluid flow at fluid intake into the pump assembly as well as through the pumping stages of the assembly. In this way, pumping efficiency of viscous or solids-laden fluid can be maximized as well, according to certain embodiments, the coupled operation of the pump assembly allows the configuration of the pump assembly to be adjusted either at intake and/or in the pumping stages to optimize performance for the particular fluids being pumped.

In particular embodiments, the submersible pump assembly comprises successive pumping stages made up of frusto-conical disk impellers separated by a diffuser to manipulate fluid flow in such a way as to generate sufficient fluid flow and pressure to pump viscous or solids-laden fluid upwardly. The pump assembly can be adjusted to accommodate the properties of the fluids being pumped. For example, the number of stages of frusto-conical disk impellers included in the pump assembly can be adjusted according to the viscosity of the fluid being pumped. Specifically, according to embodiments, the number of stages can be increased to accommodate increasing viscosity of the fluid.

The pump assembly further comprises a helical inducer coupled to the shaft at the upstream end disposed between the intake and the plurality of pumping stages. The helical inducer comprises at least a single helical turn that directly converges with the plurality of pumping stages. This configuration, according to the embodiments described herein, causes solids at the intake of the fluid to be homogenized and the homogenized fluid to be directed into the pumping stages. Specifically, the helical inducer breaks up any solids in the fluid while accelerating and directing the fluid into the plurality of successive pumping stages. According to preferred embodiments, the helical inducer directs the fluid into the eye of the impeller. The helical inducer can further be adjusted to accommodate the fluids being pumped. Specifically, the number of helical turns in the inducer can be adjusted to increase or decrease the vortical force generated by the inducer. According to certain embodiments, the number of helical turns in the inducer may be adjusted to the number of stages in order to achieve sufficient fluid flow and pressure.

Definitions

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the term “viscous and/or solids-laden fluid” refers generally to fluids containing solid particles. The term, in particular embodiments, refers to fluids produced from an underground reservoir such as heavy oil bitumen which typically will include other liquids, gases, and solid particles in fluid admixture with the bitumen.

According to certain embodiments, viscous fluids includes fluids having a viscosity of 1000 cp or greater. According to other embodiments, solids-laden fluid includes fluids having a solids content of greater than trace levels of solids such as sand, for example.

As used herein, the term “about” refers to an approximately +/−10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

Submersible Pump Assembly-Coupled Control

Embodiments of the present disclosure will now be described by reference to FIGS. 1 to 7B, which show representations of the submersible pump assembly 50 according to the present disclosure. For convenience and ease of reference, the orientation of the pump assembly 50 is referred to as being vertically arranged with the fluid moving upwardly. It will be understood, however, that the pump assembly 50 may also be positioned in other orientations without limiting the scope of the invention.

Referring to FIG. 1, a submersible pump assembly 50 of the present disclosure is configured for coupled operation of successive pumping stages 95 with a helical inducer 110 that together operate to create sufficient fluid flow and pressure to upwardly pump a viscous or solids-laden fluid. According to certain embodiments, the dual configuration allows the pump assembly 50 to be adjusted at fluid intake and/or during the pumping stages to optimize performance for the particular fluids being pumped.

As illustrated in FIG. 1, a submersible pump assembly 50 of the present disclosure comprises a cylindrical housing 60 having an intake disposed at an upstream end for receiving viscous and/or solids-laden fluid and an outlet disposed at a downstream end opposite the intake for discharging the fluid to the surface, for example. A rotating shaft 80 extends through the cylindrical housing 60 along a center axis of the housing 60 and is adapted to be driven by a submersible motor (not shown). A plurality of successive pumping stages 95 is disposed in a co-axial arrangement along the rotating shaft 80.

Positioned at the upstream end, disposed between the intake and the plurality of pumping stages 95, is a helical inducer 110 coupled to the shaft 80. The helical inducer 110 comprises at least a single helical turn that directly converges into the plurality of pumping stages 95. In contrast to prior art assemblies, it has been found that direct convergence of the helical inducer 110 with the downstream plurality of successive pumping stages 95 allows solids-laden fluid to be homogenized and accelerated into the intake of the pumping stages 95 with a reduced risk of the solids being propelled to the outer circumference of the inducer 110 causing jamming or clogging of the pump 50. According to certain embodiments, the direct convergence of the helical inducer 110 with the downstream plurality of successive pumping stages 95 allows solids-laden fluid to be homogenized and accelerated into the eye of the diffuser and/or impeller of the pumping stages 95.

The helical inducer 110 may be coupled to the shaft 80 in any suitable manner so as to rotate with the shaft 80. As illustrated in FIGS. 4B and 6B, the helical inducer 110 can comprise a cylindrical axis 150 having a central bore 130 sized to fit onto the rotating shaft 80 of the pump assembly 50. In this way, the helical inducer 110 can be co-rotated with the pumping stages 95 disposed downstream from the helical inducer 110. The helical inducer 110 is positioned below the first impeller 90 at the upstream end of the pumping stages 95 and directly above the housing intake. According to certain embodiments, as illustrated in FIG. 1, the helical inducer 110 may be disposed within a spacer 100 that extends along the length of the housing 60 to form an annulus for fluid flow.

Helical inducers 110, according to embodiments of the present disclosure, may comprise multiple helical turns. As illustrated in FIGS. 4A, 4B, 5A, and 5B, the helical inducer 110 may comprise a single helical turn 120 or more than one helical turn as shown in FIGS. 6A, 6B, 7A, and 7B which illustrate a double helical turn 160. The number of helical turns in the helical inducer 110 can be adjusted as required by design/implementation requirements. For example, according to certain embodiments, the number of helical turns in the helical inducer 110 will be adjusted in accordance with the properties of the fluid being pumped. According to other embodiments, the number of helical turns in the helical inducer 110 will be adjusted to the number of impellers 95 in the pumping stages 95 in order to achieve the desired fluid flow and pressure for the particular fluid being pumped. According to certain embodiments, the helical inducer 110 comprises a plurality of helical turns. In other embodiments, the helical inducer 110 comprises at least a double helical turn. In further embodiments, the helical inducer 110 comprises a single helical turn.

The helical inducer 110 may have varying pitches and inducer vane lengths 140 which may vary depending on varying well conditions and implementations. According to certain embodiments, the helical inducer 110 can comprise a pitch to diameter ratio ranging from about 1:0.30 to about 1:0.95. According to other embodiments, the helical inducer 110 can comprise a pitch to diameter ratio of about 1:0.45 to about 1:0.85. According to further embodiments, the helical inducer 110 can comprise a pitch to diameter ratio of about 1:0.55 to about 1:0.80. According to other embodiments, the helical inducer 110 can comprise a pitch to diameter ratio of about 1:0.65 to about 1:0.75. According to further embodiments, the helical inducer 110 can comprise a pitch to diameter ratio of about 1:0.8.

Similarly, the helix angle of the helical inducer 110 can vary depending on varying well conditions and implementations. According to certain embodiments, the helical inducer 110 can comprise a helix angle of between about 15° to about 45°. According to other embodiments, the helical inducer 110 can comprise a helix angle of between about 18° to about 35°. According to further embodiments, the helical inducer 110 can comprise a helix angle of between about 20° to about 30°. According to other embodiments, the helical inducer 110 can comprise a helix angle of about 20°.

Directly downstream from the helical inducer 110 is disposed the pumping stages 95. According to preferred embodiments, each pumping stage comprises a frusto-conical disk impeller 90 and a diffuser 70. In particular, the inventor's prior art frusto-conical disk impeller 90 (described in U.S. Pat. No. 6,227,796) is positioned within the pumping stages 95 of the present disclosure. As shown in FIGS. 2A and 2B, the frustoconical disk impeller 90 comprises a stack of axially spaced apart circular disks 13 of progressively decreasing radii towards the downstream end. Each disk 13 extends radially and concentrically from a cylindrical core 11 having a central bore 14 for receiving the rotating shaft 80 therethrough. The cylindrical core 11 comprises a plurality of parallel flow passages 17 spiraling axially about the exterior of the cylindrical core 11 which communicate with a plurality of radial flow passages 26 formed between the disks 13.

As further illustrated in FIGS. 3A and 3B, a plurality of parallel spiralling slots 17 are formed in the annular wall 16 of the cylindrical core 11 to form the axial fluid flow passages. The slot's inside radius 18 is closed at the cylindrical core and the slot's outside radius 19 is open. The slots 17 are open at the lower end of the cylindrical core 11 to form fluid intakes 20. The slots 17 are blocked at the core's upper end 21 so as to prevent axial exit of fluid from the axial flow passages 17. The number of slots 17 (seven slots shown in FIGS. 3A and 3B) and angle of advance from the axis can be varied in response to the viscosity of the fluid being pumped. For example, flatter angles (greater angle measured from the axis) are used in the case of more viscous fluid.

Each stage is separated by a diffuser 70 positioned between stages to direct fluid into the frusto-conical disk impeller 90 of the next stage. As generally shown in the exemplary embodiment illustrated in FIG. 1, each diffuser 70 comprises a stationary and inwardly spiraling vane located between top 31 and bottom 32 plate structures. The bottom plate 32 has a lesser diameter than the housing 60 to allow fluid intake at its outer circumference. Fluid is constrained by the top plate 31, engages the diffuser 70 and is driven spirally inwardly. The top plate 31 has a concentric hole at its center for discharging the re-directed fluid at the cylindrical core 11 of the next stage. In this way, fluid is drawn from the outer circumference of the pumping stages 95 and is driven radially inwardly to the intake of the next stage. By manipulating the flow of fluid through the successive pumping stages 95, kinetic energy of the fluid is exchanged for static pressure.

Operation-Directed Fluid Flow

The pump assembly 50 according to embodiments described herein provides a coupled approach to manipulating fluid flow in order to generate sufficient fluid flow and pressure to pump viscous or solids-laden fluid. Specifically, fluid flow is manipulated at intake as well as through the pumping stages of the assembly.

In operation, the helical inducer 110 breaks up solids contained in the solids-laden fluid to homogenize the fluid to facilitate intake. As the shaft 80 is rotated, the helical inducer 110 creates vortical forces in the fluid that allow suspension of the solids in the fluid to be maintained. The vortical forces further create a whirlpool effect in the fluid that directs the homogenized fluid into the eye of the impeller 90. Direct convergence of the helical inducer 110 with the upstream end of the pumping stages 95 ensures that the fluid remains homogenized when entering the eye of the impeller 90. Furthermore, the helical inducer 110 accelerates the velocity of the fluid entering the pump assembly 50 to provide additional pressure at intake.

The impeller 90 is disposed on the same rotating shaft 80 as the helical inducer 110 and, therefore, co-rotates with the helical inducer 110. Rotation of the impeller 90 further imparts energy into the fluid as it is further driven into the pumping stages 95. Within the pumping stages 95, fluid continues to flow generally upwardly through the annular flow passage 16. Between stages, fluid flow is redirected radially inwardly again to reach the fluid inlets 20 of the next stage immediately above. In this way, head losses caused by turbulence and rising back-pressure in the annular flow passage 16 is reduced as fluid pressure accumulates with each successive pump stage.

In this way, the fluid flow is manipulated at two points of operation in the submersible pump assembly of the present disclosure, at intake and through the pumping stages of the assembly to provide a coupled approach to generating sufficient fluid flow and pressure to pump viscous or solids-laden fluid.

To gain a better understanding of the invention described herein, the following examples are set forth. It will be understood that these examples are intended to describe illustrative embodiments of the invention and are not intended to limit the scope of the invention in any way.

EXAMPLES Example 1 Prototype Studies

Quantitative tests of a prototype of the frusto-conical disk pump with inducer were conducted at the Borets-Weatherford test facility in Nisku, Alberta, in order to demonstrate the effectiveness of the pump design.

The design of the frusto-conical disk pump with inducer is centrifugal, bottom driven with ESP motors, and can be staged to increase the lift. The pump was designed to keep the fluid in the laminar flow regime and thereby pump viscous and sand-laden fluids. By keeping the fluid in the laminar flow regime, a decrease in the erosion of the impellers due to sand is expected.

A cross section of the prototype pump is shown in FIG. 1. The non-directional design of the disk impellers allow the pump to be operated in both directions. The spacing between the individual disks in the impeller can be modified to suit the viscosity of the fluid being pumped. For example, larger spacings can be designed to efficiently move higher viscosity fluids.

The disk spacing of the prototype was designed for an elevated viscosity fluid. The pump was tested with and without an inducer at the intake of the pump (FIG. 1), wherein the design of the inducer resembles a machined auger attached to the pump shaft. The inducer was designed to ensure that the first stage of the pump would not have intake flow restrictions. The effect of the inducer was tested in combination with a standard diffuser and with a modified diffuser that had larger openings in the vanes.

The prototype pump was tested with water on a 250 hp test bench in the Borets-Weatherford ESP test facility in Nisku, Alberta. The prototype pump comprised 8 stages and was expected to produce 11-15 feet of lift per stage with water. An increase in lift was expected when pumping viscous fluids. The pumps were tested at a standard speed of 3500 RPM.

Results Performance and Efficiency-Effect of Inducer at Intake

Performance curves for the three pump configurations studied are shown in FIG. 8; namely, (1) disk pump with an inducer and a standard diffuser 200, 400, (2) same disk pump without said inducer 220, 420; and (3) same disk pump with said inducer and a modified diffuser 210, 410.

The disk pump configuration having (1) the inducer and the standard diffuser appears to be the preferred design since it demonstrated higher lift and flow rates, as well as better system efficiencies, under the same conditions, as compared to configurations (2) and (3). Although issues with a back pressure valve on the test bench prevented this particular configuration from being tested at no load conditions, it is expected that in a no load situation, this configuration could produce up to 180-190 m³/D (1160BPD).

Because the spacings between the disks on the impeller were sized for viscous fluids and not ideal for pumping water, which was used in these tests, the maximum system efficiency was relatively low at approximately 13%. System efficiency is expected to be better with viscous fluids. The head of 15-20 feet per stage with water with regard to configuration (1) was better than predicted.

Performance and Efficiency-Effect of Rotation Direction

While the disk impeller can be operated in both directions, it was demonstrated that there is some directionality to the pump design (1) (FIG. 9), wherein the pump includes an inducer and a standard diffuser. As such, the performance suffers when running one direction over the other. In this case, spinning clockwise 500, 600 from the intake produces better performance.

The disclosures of all patents, patent applications, publications and database entries referenced in this specification are hereby specifically incorporated by reference in their entirety to the same extent as if each such individual patent, patent application, publication and database entry were specifically and individually indicated to be incorporated by reference.

Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims. 

1. A submersible disk-type staged pump assembly for pumping a viscous or solids-laden fluid upwardly, comprising: a cylindrical housing having an intake disposed at an upstream end and an outlet disposed at a downstream end opposite the intake; a rotating shaft extending through the cylindrical housing along a center axis of the housing and adapted to be driven by a submersible motor; a plurality of successive pumping stages disposed along the rotating shaft in a co- axial arrangement, each pumping stage comprising a frusto-conical disk impeller and a diffuser; and a helical inducer coupled to the shaft at the upstream end disposed between the intake and the plurality of pumping stages, the inducer comprising at least a single helical turn that directly converges into the plurality of pumping stages.
 2. The submersible pump assembly according to claim 1, wherein the frusto-conical disk impeller of each pumping stage comprises a stack of axially spaced apart circular disks of progressively decreasing radii towards the downstream end, each disk extends radially and concentrically from a cylindrical core for receiving the rotating shaft therethrough, the cylindrical core comprises a plurality of parallel flow passages spiraling axially about the cylindrical core which communicate with a plurality of radial flow passages formed between the disks, wherein fluid flows from the upstream end of the impeller through the axial flow passages and into the radial flow passages between disks.
 3. The submersible pump assembly according to claim 1 or 2, wherein the diffuser is positioned between stages to direct fluid into the frusto-conical disk impeller of the next stage.
 4. The submersible pump assembly according to any one of claims 1 to 3, wherein the helical inducer comprises a plurality of helical turns.
 5. The submersible pump assembly according to any one of claims 1 to 3, wherein the helical inducer comprises at least a double helical turn.
 6. The submersible pump assembly according to any one of claims 1 to 3, wherein the helical inducer comprises at least a single helical turn.
 7. The submersible pump assembly according to any one of claims 1 to 6, wherein the helical inducer comprises a pitch to diameter ratio of about 1:0.8.
 8. The submersible pump assembly according to any one of claims 1 to 7, wherein the helical inducer comprises a helix angle of about 20°.
 9. A submersible pump assembly for pumping a viscous or solids-laden fluid upwardly, comprising: a cylindrical housing having an intake disposed at an upstream end and an outlet disposed at a downstream end opposite the intake; a rotating shaft extending through the cylindrical housing along a center axis of the housing and adapted to be driven by a submersible motor; a plurality of successive pumping stages disposed along the rotating shaft in a co- axial arrangement, each pumping stage comprising a frusto-conical disk impeller and a diffuser, the frusto-conical disk impeller comprising a stack of axially spaced apart circular disks of progressively decreasing radii towards the downstream end, each disk extending radially and concentrically from a cylindrical core for receiving the rotating shaft therethrough, the cylindrical core comprising a plurality of parallel flow passages spiraling axially about the cylindrical core and communicating with a plurality of radial flow passages formed between the disks, wherein fluid flows from the upstream end of the impeller through the axial flow passages and into the radial flow passages between disks; and a helical inducer coupled to the shaft at the upstream end disposed between the intake and the plurality of pumping stages, the inducer comprising at least a single helical turn that directly converges into the plurality of pumping stages.
 10. The submersible pump assembly according to claim 9, wherein the diffuser is positioned between stages to direct fluid into the frusto-conical disk impeller of the next stage.
 11. The submersible pump assembly according to claim 9 or 10, wherein the helical inducer comprises a plurality of helical turns.
 12. The submersible pump assembly according to claim 9 or 10, wherein the helical inducer comprises at least a double helical turn.
 13. The submersible pump assembly according to claim 9 or 10, wherein the helical inducer comprises at least a single helical turn.
 14. The submersible pump assembly according to any one of claims 9 to 13, wherein the helical inducer comprises a pitch to diameter ratio of about 1:0.8.
 15. The submersible pump assembly according to any one of claims 9 to 14, wherein the helical inducer comprises a helix angle of about 20°.
 16. A method for pumping a viscous or solids-laden fluid upwardly, comprising: providing the submersible pump assembly according to any one of claims 1 to 15 and a motor configured to drive the pump assembly; positioning the submersible pump assembly in a wellbore; activating the motor to actuate the submersible pump assembly; wherein viscous or solids-laden fluid enters the submersible pump assembly to be homogenized by the helical inducer to break up any solids in the fluid while accelerating and directing the fluid into the plurality of successive pumping stages.
 17. The method according to claim 16, wherein rotation of the helical inducer creates a vortex at the intake of the submersible pump assembly. 